caching of packages in remote repository

Configuration option to keep a local mirror of installed packages from remote repository, and to allow reboot using those packages (if running in-memory from usb-stick/compact flash).

(from redmine: issue id 49, created on 2009-06-23, closed on 2009-07-07)

• Changesets:
  • Revision 233918e5 by Timo Teräs on 2009-06-29T06:29:57Z:

db: cache packages (ref #49)

If /etc/apk/cache is a symlink to directory, a copy of all installed
packages is stored there, and the index of remote repositories will
be there instead of /var/lib/apk. This enables to reconstruct running
system during boot.

Left as todo: remove cached copy when the package is removed, and
additional apk applet to download missing packages to cache and/or
remove extra items.

• Revision 9858ffff by Timo Teräs on 2009-06-29T08:22:55Z:

cache: new applet (ref #49)

Administrative tool to download or delete files to/from the cache.

• Revision b551c3b0 by Timo Teräs on 2009-07-07T06:33:13Z:

cache: use changeset to figure out downloadables

that way we get the same result as the 'apk add world' at boot
time; it might differ from currently installed set (ref #49).

• Revision dc5c436c by Timo Teräs on 2009-07-07T06:40:59Z:

cache: delete also wget temporary files

check for the full filename to match an expected pattern or
delete it (so we delete files with .new, .new.backup, etc.).
final part of remote package caching: fixes #49.